Fluid agricultural fertilizers include manure, sewerage and septage and chemical fertilizers with a solids content under about 13 percent by weight. Application of such fluid fertilizers may be done by flood irrigation, aerial spraying, irrigation sprayers, mobile surface sprayers (tank-type or drag hose type, either of which may incorporate tillers to incorporate the liquid into the soil), and fluid injectors. Fluid injector applicators typically use a shank to loosen and create voids in the soil so that the liquid fertilizer may be injected into the soil immediately behind the shank. Gaseous anhydrous ammonia may be injected in the same fashion. These systems can leave fluid at the surface if the voids created below the surface are not large enough to accept the volume of fluid injected.
Fluid agricultural fertilizer application methods have many disadvantages, both in cost and effectiveness. Flood irrigation, aerial spraying, and irrigation sprayers have significant costs and are limited by the configuration or topography of the fields. Liquid manure or treated sewerage fertilizer may produce significant malodors. Mobile surface spraying and fluid injectors are costly because they require large volumes of liquid to be transported to the application site, and the volume of fluid to be applied limits the amount of solid nutrients which may be applied at one time. Tank surface sprayers cause soil compaction and high fuel costs due to the weight of the fluid necessarily carried. Drag hose surface spraying is often impractical on sloped or irregularly-shaped fields. As the solid content of fluid agricultural fertilizer increases, fluid application systems become prone to malfunctions and may require special pumps. Fluid systems may also require agitation to keep solids in suspension. Mobile spraying applications often require tilling to incorporate the fertilizer into the soil and to reduce malodors. Fluid injection applicators, such as that described in U.S. Pat. No. 5,865,131 (Dietrich), have been developed to place the liquid below the surface and reduce the need for tilling, but many of the problems of fluid application methods remain: large volumes of fluid to transport, limited amounts of nutrients which may be applied at one time, soil compaction, and difficulty accepting higher solid content. For treated sewerage, environmental regulations often limit where fluids may be applied because of malodors or the potential for the fluid to migrate to watercourses.
Conventional fluid injection systems are not generally adapted for the injection of high-pressure fluids. Such systems, with a tubular injector mounted behind a shank, are also not adaptable to the application of viscous fertilizers, in part because sufficient void space is not maintained below the surface of the soil to accept the viscous fertilizer, in part because they do not operate at high enough pressure, and in part because the equipment may not be adapted to the solids content of viscous fertilizers.
Between about 13-40% solid content by weight, fertilizers, soil amenders, and soil conditioners are viscous, and the term “viscous fertilizer” in this disclosure includes such a range of solid content. However, the apparatus and methods described are effective on a wider range of materials, and the term “viscous fertilizer” as used in this disclosure also refers to fertilizers, soil amenders, and soil conditioners with a solid content falling within a range whose lower limit is from 0% to 40% and whose upper limit both is above the lower limit and is from 13% to 52%. “Viscous fertilizers” include, but are not limited to, biosolids, dewatered biosolids, sewage sludge, manure, slurries, or other chemical or mineral fertilizers in the 0-52% solid content range.
Viscous fertilizers above about 13% solid content have traditionally been applied by manure spreaders that involve an open-topped hopper, a conveying mechanism (e.g, augers, a conveyor belt floor, a live bottom floor, a walking floor, an apron chain, or a push blade) which conveys the viscous fertilizer to an open end or side of the hopper where rotating tines fling the material into the air, from which it falls onto the surface of the ground. A second pass over the application area is often required to till the material into the soil and to mitigate malodors. Such viscous fertilizers may also be applied in bulk and then spread with earthmoving equipment. All these methods may result in uneven application of the viscous fertilizer and repeated and costly reworking of the soil.
Fertilizers, soil amenders, and soil conditioners with higher solids contents may be applied as are viscous fertilizers. They may also be supplied in granular or pellet form, in which case they may be applied with a centrifugal spreader.
The use of biosolids for fertilization, soil amendment, and/or soil conditioning presents particular problems. At a sewerage treatment plant, for example, biosolids are found in sewerage at only a few percent solid content by weight. However, the cost of transporting the great quantities of such fluid required and the difficulties in the agricultural application of such a fluid to the soil generally make it more efficient to dewater the biosolids before their use in agriculture.